xfs_scrub: use datadev parallelization estimates for thread count

During phases 2-5, xfs_scrub should estimate the level of
parallelization possible on the data device to determine the number of
threads spawned to scrub filesystem metadata, not just blindly using the
number of CPUs.  This avoids flooding non-rotational storage with random
reads, which totally destroys performance and makes scrub runtimes
higher.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/scrub/phase1.c b/scrub/phase1.c
index 2113014be6ed9dd87034dd483aacda91f9790a56..6b472147f866386f17acb039ff4f25d6bae0d9eb 100644 (file)
--- a/scrub/phase1.c
+++ b/scrub/phase1.c
@@ -109,13 +109,6 @@ _("Must be root to run scrub."));
                return false;
        }
 
-       ctx->nr_io_threads = nproc;
-       if (verbose) {
-               fprintf(stdout, _("%s: using %d threads to scrub.\n"),
-                               ctx->mntpoint, scrub_nproc(ctx));
-               fflush(stdout);
-       }
-
        if (!platform_test_xfs_fd(ctx->mnt_fd)) {
                str_info(ctx, ctx->mntpoint,
 _("Does not appear to be an XFS filesystem!"));
@@ -193,6 +186,13 @@ _("Unable to find realtime device path."));
                return false;
        }
 
+       ctx->nr_io_threads = disk_heads(ctx->datadev);
+       if (verbose) {
+               fprintf(stdout, _("%s: using %d threads to scrub.\n"),
+                               ctx->mntpoint, scrub_nproc(ctx));
+               fflush(stdout);
+       }
+
        if (ctx->fsinfo.fs_log) {
                ctx->logdev = disk_open(ctx->fsinfo.fs_log);
                if (error) {